Hilbert-Transform-Based Transient/Intermittent Earth Fault Detection in Noneffectively Grounded Distribution Systems

Conventional relaying algorithms are mostly based on phasor computation. Since it is difficult to obtain accurate phasor results in fast transient situations, most of the feeder relays fail to correctly respond to transient/intermittent earth faults, which are, however, frequent fault cases in distribution systems. This paper presents a novel approach for fault detection and direction determination for these transient/intermittent faults. The basic idea is to extract the fault direction using the instantaneous power's direction. The instantaneous power is obtained by using Hilbert transform. The proposed direction element inherently utilizes the high-frequency components of the transient fault signals at a conventional sampling rate. Together with an intermittence detection algorithm, a scheme for transient/intermittent earth fault detection has been proposed. It has been implemented as a prototype relay. Electromagnetic Transients Program tests as well as physical model tests have proved the effectiveness of the proposed scheme.